Raw shale oil sometimes contains nitrogen or nitrogen containing compounds, all hereinafter collectively referred to as "nitrogen", and/or impurities such as arsenic and/or selenium and compounds of arsenic and/or selenium, all hereinafter collectively referred to as "impurity" or "impurities". Both nitrogen and impurities are desirably removed or at least minimized in the final shale oil product.
It can be expensive to remove nitrogen and impurities and therefore it is highly desirable to remove the maximum amount of nitrogen and impurities at minimum processing expense.